After the massive difference in the poll, the 10mm being favored between the two options I had (310mm unsupported XRod length), I have taken the task to “port” the previous 8mm design to 10mm and I must say it wasn’t at all easy. I am not the best CAD designer but this wasn’t about CAD, was about keeping the size as compact as possible as well as the features that I have imprinted into the concept.
So this 10mm variation is a bit bulkier, ~73mm compared to 60mm in length that the 8mm version had, while the rest is just the same. I managed to keep the hotend at the same level, the belt catchers in the same place, basically this is a drop-in replacement (YCarriages need to be re-printed as they are also redesigned to receive the 10mm rods but the re-design is minimal).
What I am not completely happy with is that I am still using bearings that have play in them (LM10UU), and that the design is a bit massive for a single hotend bowden setup.
What do you think? Comments are greatly appreciated.
Unfortunately the high end precision bushings and the adjustable tension bearings (Thomson Super10) are out of our reach and they are not sold in enough quantities to mere mortals to have their price drop like the linear guides are starting to. So the alternative would be block bearings on linear guides… but not yet for me.
I am not aware of the tolerance and wear resistance differences between bushings and LM[…]UU linear bearings but there is a situation when I would consider using them. That is to use 3 short ones per rod and bias them against the rod with tensioners so that any play is taken out of the system.
@Florian_Ford Please take the following as a try of contructive criticism and not wanting to offense, I write it with a smile on the face and I really cherish your time and the effort you put into this design. I for myself did build 4 coreXY on my own and the last two are completely own design even without some “stolen ideas”. So, I know what work a desing is and just want to share some thoughts between fellows… So let’s go: On the first glance, this looks overengineered. A desing is best, when it is simple. While I notice some nice details like the pushing screws to prevent the Y-carriages to get pulled into the middle by belttension, what shows that you are aware of some of the hidden difficulties of a coreXY system, there are some other things that really need some revision.
First: These parts look very hard to print. I question that you even thought about designing the parts with a single thought at printing them later on. Why it surely isn’t impossible to print this, it shows skill to design parts or things with more than function in mind.
Second: What I really don’t like is the way you mount and cool the hotend. This is not easy accessible, the lower ones of the cooling fins are not cooled well (and these are the important ones!) and the design will cause the airflow to build up such a big backpressure, that there is probably no (noticeable) airflow at all (the air needs to go somewhere) and not through the fins, too. Not to mention that the whole flat X-carriage is merely not even 5mm above the printarea (guessing from pictures).
Then the bearings in the corners. Please think about supporting their axis on both sides, top and bottom. This, like you show it now, is printed plastic and it is going to flex. A lot.
A well-meaning advice is to look at other likely similar designs like a “sparkcube”. I do not say, that this one is better or not. It is just one of the better designs I know about. I just want you to look and check other solutions of a coreXY-system and learn of and/or improve their ideas. Feel free to contact me for deeper conversation about this. Cheers!
@Rene_Jurack No offense at all I am glad somebody takes the time to constructively criticize my design. This is the exact conversation that I would like to have.
I am aware of many of the flaws of the design, it’s a WIP after all but I intend to print it. I find it quite complex myself but simplifying it is no easy task.
Let’s take your concerns one by one:
“the lower fins are not cooled well” - true, right now I got rid completely of the ring around the hotend, as it bears no actual functionality besides offering some strength to the part. Now I have a big hole in which the hotend is clamped by the upper “normal” mount and the 4 screws pushing it into place.
“backpressure” …my intention was to have one fan push air while the other extracts it … I am not at all sure that will work but I didn’t intend to push air from both sides.
“supporting the bearings axes in both sides” … I am guessing you are referring to having clamps at both ends of each bearing. Here again I am aware of it but I am trying a bit of “kludge” thingking. The bearings will deviate a bit off their axis due to single-side-clamping and will “slightly bind”, taking away the play their better of worse tolerances allow. This is not engineering thinking I know, but I find it a way to improve on a cheaper design.
oh man I am looking at them like crazy… Like I said I know most of the flaws, the tricky part is to solve them in a cost-effective (read: cheap) way.
Thanks again for chiming in and I like the idea of a deeper conversation should you find the time.
Ok, pushing in and sucking out the air will definitively be better. But you really need to cool the lower fins!
In a coreXY the length of the belt is your enemy. Flexing bearings in the corners make this even worse. You need to get as much stiffness to the “non-moving” parts as possible. Otherwise you throw away one of the advantages of the coreXY-system.
Instead of fixing the coldend with 4 screws from all sides, why not just print a ring around it at the bottom? This way you can direct the airflow better and the complete hotend is fixed too.
So, getting direct airflow to the lower fins is tricky. I was betting on the indirect turbulent air flow resulted from the angled fans in this design. Will have to ponder more on this one.
I didn’t try a 3d-printed piece clamping the lower fins because of heat creep. 4 bolts seemed like a better way to clamp the hotend from a more remote area.
Regarding the bearings being slightly off-axis being such a bad idea … I get it from an engineering pov but I see it as a way to take wiggle out of the tolerance in the bearings… should the bearings be completely straight the play in the bearings will be awful. With the LM10UUs that is. I can’t really justify buying Thompson super10 or the like so I somehow have to fight this mcguyver-ish.
@Florian_Ford A little Super Lube oil on the rods and I doubt you could wear out SF1s on a printer. The SF1s that I have press fit have less play than lm8uu.
SF1 or Graphite Lubricating Brass Bushings? I like SF1 because they are very slim. Is there any link to see your machine or the way you are using the SF1s?
I had a machinist friend make Delrin lm8uu adapters on a CNC lathe. I use them on my p3+ (steel). I have printed (and reamed with a 10mm bit) adapters for my bosses p3+ but he hasn’t used them yet. I experimented with press fitting Igus J bushings in different sized holes to get a good fit. It was hit and miss. They may work with a clamping design like yours, where you can adjust the fit on each bushing when assembled. I decided to play with sf1s because they were cheaper than bronze/oillite(sp?)
I was wondering if with SF1 bushings soft steel shafts or even aluminum shafts can’t be used … they surely look like a good prospect because there is no steel balls rolling into their surface …
I am considering SKF dry bushings for my cartesian design (they use bronze with a PTFE filler in the voids) in order to avoid the need for oiling the rods. The small print for these bushings indicates that they are not ideal for radial loads. Is this a general thing for bushings or unique to this type?
There is one other option that I could try. That is take open bearings and use tension adjusting carriage to squeeze those until play is eliminated. That’s one reason I am going to keep this 10mm design, otherwise I am going to try the SF-1 self-lubricating bushings (maybe sintered bronze ones later on).
